The invention relates to a method and arrangement for cleaning pipe-shaped filter elements through which raw gas is conducted from a raw gas space into a clean gas space, in which a safety filter is disposed. The filter elements are cleaned by backflushing from the clean gas space. As filter elements, mainly tube-like filter cartridges as they are used for the hot gas filtration are considered herein but the method is applicable to all tubular or hollow cylindrical filter elements.
In conventional filter cleaning systems, the cleaning intensity is limited by the speed of sound as upper limit for the cleaning gas flow through the filter channels. Since in filter cartridges, the pressure which is necessary for the dislodging of the deposits is derived from the kinetic energy of the gas flow, the obtainable pressure is limited. The operational behavior is further deteriorated when the filter has a high flow resistance for example by fine dust particles lodged in the filter, by a high dust content or by high filtration speeds. It is therefore difficult or impossible to clear filters by back flushing once they are clogged.
The method according to the present invention is specifically concerned with the high temperature particle filtration particularly of ceramic filter cartridges. Of particular concern is the protection of the plant during cleaning especially if a filter element breaks during cleaning.
For cleaning the filter elements or cartridges, it is presently common practice to apply pressure pulses at the clean gas side of the filters. However, with long filter cartridges with small inner diameters only relatively small cleaning effects can be achieved at the ends of the cartridge. In principle, the pressure of the flushing medium must be twice the pressure of the system during normal filtering operation in order to achieve a good cleaning effectiveness. Usually the pressure during filtering operation is 6 bar. In the pressurized coal conversion, the cleaning pressure to which cleaned product gas or N2 is to be compressed must be between 15 and 60 bar to provide an appropriate cleaning gas pressure. Furthermore, breakage of a filter cartridge results in high dust emissions whereby the dust can be carried in combined gas/steam turbine plants into the gas turbine resulting in damage to the gas turbine. It is therefore desirable that means are provided which permit continued power plant operation even if a filter cartridge breaks. To achieve this, generally there is provided a second filter stage in the form of a safety filter arranged in the gas flow downstream of the filter cartridge.
EP 0 551 951 A1 discloses such a method for filter cartridges through which raw gas flows from the outside to the inside wherein a safety filter is arranged in the clean gas space downstream of each filter cartridge. Cleaning of the filter cartridge is achieved by back flashing of the filter cartridge from the clean gas space by a gas jet entering the filter cartridge. This however, does not result in a good cleaning of the filter cartridge. In addition, there are cleaning gas losses through the safety filter.
It is therefore the object of the present invention to provide a method for the cleaning of filter cartridges with which, on one hand, the cleaning of the filters is improved and which, on the other hand, provides for the cleaning of the filter cartridges even if a filter cartridge or a row of filter cartridges breaks, without a carryover of contamination into the clean gas flow.
In a method and apparatus for cleaning pipe-shaped filter elements arranged in a housing including a separation wall dividing the housing into a clean gas space and a raw gas space into which the filter elements extend from the clean gas space through the separation wall and the raw gas is directed from the raw gas space through the filter elements into the clean gas space while dust is removed from the raw gas and collected on the filter elements, the filter elements are cleaned from time to time by supplying momentarily pressurized flushing gas to the clean air space which, at the same time, is closed to generate a flushing gas pulse providing for a backflow of clean gas from the clean gas space to the raw gas space, which dislodges dust collected on the filter elements.
Details of the invention will become apparent from the following description thereof on the basis of the accompanying drawings.